The phrase "an unprecedented task" is correct and usable in written English.
It can be used to describe a task that has never been done before or is unlike any previous tasks in terms of difficulty or scope.
Example: "The team was faced with an unprecedented task of developing a vaccine in record time."
Alternatives: "a unique challenge" or "an unparalleled undertaking".
At the same time, he faces an unprecedented task in terms of reassuring an anxious city and capitalizing on the good will of the rest of the country.
The sweeping overhaul of financial regulations passed into law last year requires agencies to write hundreds of rules, an unprecedented task, even as they grapple with the unfamiliar financial landscape left by the crisis.
After ruling Mexico since 1929, the party faces an unprecedented task: it must not only find new leaders, but a new identity and methods to sustain it in opposition.
In South Sudan, for example, the mission is sheltering over 200,000 civilians within its camps -- an unprecedented task.
B7 The Aftermath AN UNPRECEDENTED TASK -- New York City police detectives and other law enforcement officials have been scouring tons of debris carted from the trade center to a 165-acre landfill in Staten Island.
This is a bold and unprecedented task, and the Moei River has become "more than a border between nations.
The committee members deserve credit for carrying out the thankless and unprecedented task of disciplining a fellow senator.
It allowed him, said Fitzgerald, to "take on this unprecedented task to expose a grievous transgression of the U.S. Constitution".
Alfred Barr Alfred Barr, MoMA's first director was aware of the unprecedented task he faced: to create a museum that was populist in spirit and in which a single story could be told of the development of art from 1880 (the approximate date at which it was agreed that "Modern Art" was first manifested) to the present and on into the future.
The joint United Nations-OPCW team is undertaking the unprecedented task of trying to eliminate a nation's chemical arsenal amid a war.
